Hi!
Metis was my first cosplay and I am currently in the process of remaking it!
I used styrene plastic to cut the shapes for the armour and spraypainted them gold. They looked great, however, cutting the shapes were a little troublesome so I am remaking them with craftfoam (which will be gessoed and painted) this time around. Also, I think I might put some wire in between the pieces of foam so that I get a little more shape and structure.
I'm pretty sure that you could use the same materials for aegis's leg armour.

For the red parts, I suggest using red cellophane or transparent red vinyl, though the latter is a bit expensive. I sandwiched the red cellophane in between two gold pieces for each piece of hip armour (there are two). I ultimately connected the armour to my suit using safety pins.

For metis's helmet, I took apart some old headphones for the base. using the same technique and materials as the hip armour, I made the face covering and two circular shapes to cover the sides of my head. the three pieces were connected together using long rectangular strips of styrene. The connected piece was then mounted onto the headphones. using old bottles, I made a small contraption so that I could have the mask over my face or on my head, if I wanted. It's a little hard to explain in words xDD I'm sorry that my explanation is lacking.

I took apart most of my helmet, but I still have one completed piece of my hip armour intact.
If you don't mind how beat and torn apart (well, this may be good so you could see process work? xDDD) my armour looks now, I wouldn't mind taking pictures of them.

I really wish that someone could have helped me while I was making this the first time around.
I really hope that this helps!